How is the 18650 lithium battery produced?

Click：1519Time：2018-07-09 08:49:42

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Lithium batteries are the most used batteries in the digital field.
Its most prominent advantage is its high energy density, which is suitable for
digital products that are very compact and portable. At the same time, compared
to the previous dry batteries, lithium-ion batteries can be recycled and have
advantages in environmental protection. Lithium-ion battery positive and
negative materials can absorb and release lithium ions. However, the potential
energy of lithium ions in the positive and negative electrodes is different.
The lithium ion chemical potential in the negative electrode is high, and the
lithium ion chemical potential in the positive electrode is low. When lithium ions
are discharged, lithium ions stored in the negative electrode are released and
absorbed by the positive electrode. Since the potential energy of lithium ions
in the negative electrode is higher than that of the positive electrode, this
potential energy difference is released as electric energy. The charging
process is a reversal of the above process, releasing lithium ions in the
positive electrode into the negative electrode. Due to the migration of lithium
ions in the positive and negative electrodes, the lithium ion battery is also
called a rocking chair battery.

The 18650 is the most common lithium-ion encapsulation method at
present, whether it is the most popular ternary material at present, or the
lithium iron phosphate that the country pushes, and lithium titanate that has
not been popular yet, all have the specification of 18650. 18650 type
batteries, Cylindrical cylindrical package, this battery core diameter 18mm,
length 65mm, widely used in charging treasure, electric cars, notebooks, light
flashlights and other fields, the benefits of such packages are unified
specifications, easy automation , Large-scale production, with high mechanical
strength, high impact resistance, high yield characteristics; In addition there
are Prismatic square soft package, common in mobile phones and tablet
computers, the most direct benefit of such a package is thin, small, portable .

In the era of notebook computers, 18650 batteries are just behind
the scenes of digital products. With the popularity of smart devices such as
smart phones and tablets, the 18650 has also begun to move from behind the
scenes to the front desk and is known to the public. So how does the seemingly
simple 18650 battery come into being and what is its secret? Next, let us
explore the birth process. I will illustrate the birth of the 18650 battery
from the three aspects of coating, assembly, and testing.

The first production process of the battery core: coating

Before entering the production floor, you need
to wear a mask and shoe cover to avoid inhalation of dust and static
electricity. First of all, from the coating process, large copper foil (yellow)
and aluminum foil (silver) can be seen in this process. Aluminum foil is used
to coat nickel-cobalt-manganese NCM ternary materials; conversely, copper foil
is used to coat negative active material graphite; white is the separator.
Global lithium battery separator is mainly occupied by Asahi, Celgard, SK,
toray, W-SCOP and other manufacturers, these foreign companies control nearly
70% of the market share. The market share of Chinese diaphragm companies
accounts for about 30%, and lithium battery separators are constantly making
localization breakthroughs. The capacity of the cell is based on the area of
the formulation of these formulations.

A complete roll of coated positive and
negative electrode material is about 126mm wide. Next, it needs to be cut into
7 small rolls with a width of about 18mm. Each roll will be evenly divided into
several sections. Each section represents the required materials for a single
cell. According to XCMG, an engineer of the cell core factory, the current
price of ternary cathode materials is 120,000 yuan per ton, which can be used
to produce 50,000 cells per ton of material. Currently, the average daily production
capacity of solar cells is 500,000, and 10 tons need to be used. Ternary
cathode material, this expenditure of light daily needs 600,000 yuan.

The automated machine will mark each section
with a nickel tape and an insulating high temperature resistant Mylar sheet.
The next step is to carry out five levels of weighing, namely, weight bias, A1,
A2, A3, and lighter. This is the same as the selection of CPU wafers. Different
physiques will appear in the same batch of cutting process. According to different
physiques, the corresponding capacity will be divided and shipped.

The second production process of the battery
core: Assembly

The well-defined positive and negative
electrodes will be fully automated here. The white material is a separator. The
battery core is still not working properly. It is necessary to add an
electrolyte as a medium to allow the positive and negative electrodes to
undergo a chemical reaction. Lithium ions can migrate between the positive and
negative electrodes, and a charged ion output energy lithium battery can be
charged and discharged. Automatic roll-packing directly on the assembly line,
into the next assembly step into the steel shell.

Steel shell is a one-piece stamping
molding, the thickness of less than 1mm, so the high strength and quality
requirements of steel, this appliance core factory is selected to import
Hansteel materials.

This step connects the negative electrode
tab to the bottom of the steel shell by spot welding. The factory uses a
Japanese Miyachi laser spot welding machine to ensure spot welding accuracy and
product quality. The spot welder can't weld the bottom of the steel shell,
insert the bottom from the reserved hole first, and then put it into the spot
welder. Squeeze it, and the negative pole will make a good nickel strip and
connect it to the bottom of the steel shell.

The electrolyte is injected into the glove
box filled with inert gas argon in a sealed box. The oxygen concentration in
the sealed box gloves must be less than 10 ppm (close to an oxygen-free vacuum
environment) to prevent electrode oxidation. The electrolyte argon gas is sent
to the sealed box through the circulating purification device. The catalyst
contains hydrogen and hydrogen, which can be removed by the reaction of
hydrogen and oxygen. At the same time, the desiccant in the device absorbs
moisture and ensures the drying of the atmosphere inside the box.

After the electrolyte is injected into the
cell, the cap and the steel shell have been joined together by laser welding.
Rows of neat and orderly piled up, ready to go.

A new battery was born. Each cell needs to
wear "new clothes" - PVC sleeves sorted by capacity.

Different capacities correspond to
different PVC jackets. Here we see green, blue, pink and other colors. The rich
appearance color adds a sense of fashion to the batteries.

The
Final production process of the battery core: First charge and test

After the electrolyte is injected into the
electrolyte, no electricity is actually stored. At this time, the states of the
positive and negative electrodes have not reached a stable state, and they must
be charged through the first charge before they can be used normally. This
first charge is called “chemical conversion”. When charging for the first time,
extra charge is required to create a protective film on the electrode surface.
This protective film is the secret of the low self-discharge of the lithium-ion
battery. At the same time, the properties of the protective film also affect
the performance and life of the battery. Therefore, the formation process is
very important. Chemical conversion is accomplished using a volumetric cabinet.

The batteries are chemicals. In order to
ensure the safety and longevity of the products, they must be packed in boxes
before packing, 200 boxes per box. Ensure three consistency: consistent
capacity, consistent internal resistance, and consistent voltage. Only in this
way can it be delivered normally, otherwise it will be thrown into the cold
room and become B-level and C-level batteries.

The first test, capacity. In order to
ensure the accuracy of the capacity test, the factory purchased the
industry-leading Bell automatic weighing cabinet to meet the needs of tens of
thousands of daily sub-capacity. The newly born batteries need to do five
cycles of burn-in tests and pick out those that cannot work or have a deviating
capacity. According to the national standard GB/T18287-2013 "General
Specification for Lithium-ion Battery and Battery Packs for Mobile
Phones", 0.2C charge and discharge tests are to be conducted. Charge with
appropriate current to 4.20V cut-off (high voltage version needs to be charged
to 4.30V or 4.35V), let stand for a period of time (more than 15min) so that
the battery temperature is close to room temperature and the polarization
within the battery is basically dissipated. The test uses a 0.2C discharge to a
2.75V termination voltage to reach the marked capacity before it is considered
qualified. Here, C is a unit of magnification, taking a 2600 mAh cell discharge
as an example, and 0.2 C as a 520 mA discharge.

The second test, internal resistance. Now
the batteries factory is equipped with internal resistance automatic screening
machines that can be screened. 18650 three yuan materials, internal resistance
within 70 milliohms, are counted as qualified products; less than 30 milliohms
is a special pick. If it is lithium iron phosphate or lithium titanate, the
internal resistance can be within 20 milliohms.

The third test, voltage. The battery
voltage in the same box is 3.7V±0.05, which is convenient for multi-section
parallel connection or series use. Each box of batteries has been made with
three consistent pairs, so it is not recommended to use across the box. This is
a common method in the world.

In addition to the conformance test, each batch
of batteries also needs to perform dozens of destructive tests, such as impact,
vibration, and puncture, to eliminate hidden dangers and ensure the best
quality of each batch.